The present invention relates to the field of implantable medical devices, more particularly, to cardiac pacing systems having nodal rhythm detection and treatment.
Implantable cardiac pacing systems deliver a pacing signal to stimulate a heart chamber. The pacing signal is typically delivered by an electrode in the heart chamber. The same electrode is also used to sense electrical activity indicating an intrinsic contraction of the heart chamber. The presence or absence of the sensed activity and the timing of the sensed contractions, are used to control the cardiac pacing system for the patient""s well being.
In AV nodal rhythm, the intrinsic AV pacemaker controls the ventricles and atria. The nodal rhythm can result from anything that suppresses sinus node activity, such as sinus bradycardia; any form of vagal stimulation; digitalis; the initial phase of atropine action; SA block; or congenital absence of the SA node. The AV nodal rate will usually be less than 50 beats per minute.
AV nodal rhythm may also occur from anything that enhances AV nodal rhythm, such as digitalis intoxication, rheumatic fever, or inferior myocardial infarction. The AV nodal rate will usually be between 60 and 100 beats per minute. This is also called accelerated AV (nodal) rhythm.
Sherlag et al. present evidence of that there are at least two varieties of AV junctional rhythm: true AV nodal rhythm of 30 to 40 bpm increased under influence of atropine, and His bundle rhythm of 20 to 25 bpm little affected by atropine. Scherlag, B. J., Lazzara, R. Helfant, R. H., Differentiation of A-V Junctional Rhythms, Circulation, 48:304, 1973.
Currently AV nodal rhythm can be treated with medication, or by cardiac stimulation. Medication may be ineffective or have undesirable effects. Surgical intervention can be used to remove or reduce the AV conduction system, but runs the risks inherent in any surgical procedure, as well as uncertainty as to result.
During AV nodal rhythm, atrial contraction takes place during ventricular contraction. The blood in the atria is forced back into the venous system and may cause clinical symptoms such as venous pulsations in the jugular area and in the abdomen. Through an increased venous pressure because of the regurgitation into the venous system, inappropriate baroreceptor reflexes may cause acute drops in blood pressure.
The most pertinent prior art references known at the present time are the following:
In xe2x80x9cTransesophageal Atrial Pacing For Intraoperative Sinus Bradycardia Or AV Junctional Rhythm: Feasibility As Prophylaxis In 200 Anesthetized Adults And Hemodynamic Effects Of Treatment,xe2x80x9d Atlee et al., J Cardiothorac Vasc Anesth 1993 Aug;7(4):436-41, Atlee et al. reported that transesophageal atrial pacing (TAP) at a rate sufficient to overdrive atrioventricular junctional rhythm (AVJR) was effective initial treatment in all patients tested. Feasibility of TAP as prophylaxis for sinus bradycardia (SB) or AVJR was tested with approved or investigational devices in 200 anesthetized surgical patients, not necessarily with cardiovascular disease or having cardiac surgery. Thirteen patients had AVJR (72+/xe2x88x924 beats/min; mean +/xe2x88x92SEM).
In xe2x80x9cThe Effects Of Overdrive Pacing And Lidocaine On Atrioventricular Junctional Rhythm In Man: The Role Of Abnormal Automaticity,xe2x80x9d Tenczer et al., Circulation 1985 Sep;72(3):480-6, Tenczer et al. reported AV junctional rhythms in group I (17 patients) were suppressed by overdrive pacing, and their rates were decreased by lidocaine. AV junctional rhythms in group II (five patients) were not suppressed by overdrive pacing. The data suggest that AV junctional rhythms in group I were caused by normal automaticity, while those in group II were probably due to abnormal automaticity.
All prior art references above are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, the Detailed Description of the Preferred Embodiments and the claims set forth below, many of the devices and methods disclosed in the prior art references may be modified advantageously by using the teachings of the present invention.
The present invention is therefore directed to providing a system and method for nodal rhythm detection and treatment. The system of the present invention overcomes the problems, disadvantages and limitations of the prior art described above, and provides a more efficient and accurate means of nodal rhythm detection and treatment.
The present invention has certain objects. That is, various embodiments of the present invention provide solutions to one or more problems existing in the prior art of nodal rhythm detection and treatment. Those problems include, without limitation: (a) need for automatic nodal rhythm detection, (b) need for automatic nodal rhythm treatment, (c) interference with intrinsic heart rhythm, (d) patient discomfort from pacemaker syndrome, and (e) patient discomfort from abrupt changes after treatment.
In comparison to known techniques for nodal rhythm detection and treatment, various embodiments of the present invention provide one or more of the following advantages: (a) the ability to automatically detect nodal rhythm, (b) the ability to automatically treat nodal rhythm using atrial pacing tuned by the AV delay, and (c) the ability to restore the intrinsic heart rhythm with an optimized hemodynamic AV delay.
Some of the embodiments of the present invention include one or more of the following features: (a) an IMD having automatic nodal rhythm detection, (b) an IMD having automatic nodal rhythm treatment that use atrial pacing tuned by the AV delay, (c) methods of performing nodal rhythm detection that use a nodal activity window, (d) methods of performing automatic nodal rhythm treatment that use atrial pacing tuned by the AV delay, and (e) methods of avoiding patient discomfort from AV nodal rhythm.
At least some embodiments of the present invention involve detecting nodal activity by looking for atrial activity in a nodal activity window around ventricular activity. If a predetermined number of successive atrial events fall within the nodal activity window, nodal rhythm is present. The nodal activity window is typically 60 ms before and 100 ms after a ventricular sense, but may be shorter and can be tuned for a specific patient. The nodal activity detection method first determines if the atrial event precedes the ventricular event (positive AV delay) or vice versa (VA delay), then looks for atrial activity between a first time limit and the ventricular activity if the atrial event precedes the ventricular event (positive AV delay), and for atrial activity between a second time limit and the ventricular activity if the ventricular event precedes the atrial event (positive VA delay). The nodal activity detection method can also calculate an appropriate initial atrial escape interval for nodal treatment if pacing is to be applied. If atrial activity occurs outside the nodal activity window before the predetermined number of successive atrial events is reached, the nodal rhythm detection counter is reset and the nodal activity detection method starts over.
Other embodiments of the present invention involve detecting nodal activity, then treating the nodal activity using pacing. The nodal rhythm detection and treatment method starts by checking for tachycardia and average ventricular rate greater than 100 beats per minute, then terminates the nodal treatment if either is found because nodal rhythm could not be occurring with those conditions. If neither condition is present, the nodal rhythm detection and treatment method checks to see if nodal treatment is active, then looks for nodal rhythm using a nodal activity detection method if it is not.
If nodal treatment is active, the nodal treatment follows different procedures depending on whether the activity is an atrial sense, an atrial pace followed by a ventricular sense, or an atrial pace followed by a ventricular pace.
An atrial sense may indicate that the nodal rhythm is in control and further adjustment of the atrial escape interval is required. The nodal treatment method looks for atrial activity in a nodal activity window around ventricular activity. The nodal activity window is typically 60 ms before and 100 ms after a ventricular sense, but may be shorter and can be tuned for a specific patient. Depending on the timing of the ventricular sense with respect to the atrial sense, the nodal treatment method calculates a new atrial escape interval to tune the atrial escape interval.
An atrial pace followed by a ventricular sense indicates that the therapy is effective. The next AV delay is further tuned based on the last ventricular sense. An atrial pace followed by a ventricular pace indicates the nodal rhythm has stopped. The pacing enters a flywheel mode in which the pacing interval is gradually increased to ease out of nodal treatment. If a predetermined number of successive atrial pace-ventricular pace sequences occur, nodal rhythm is no longer present and the nodal treatment is deactivated.